Architectural finish



United States Patent Ofiice 3,051,080 Patented Aug. 28, 1962 3,051,080ARCHITECTURAL FINISH Francis J. Clarke, Leechburg, Pa., assignor toAllegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation ofPennsylvania No Drawing. Filed Nov. 8, 1960, Ser. No. 67,889 6 Claims.(Cl. 101-32) This invention relates to improvements in the surfacefinishes for stainless steel and is particularly directed to a newarchitectural finish for austenitic stainless steel panels.

In modern architectural design of buidings and particularly commercialoifice and business buildings in metropolitan areas, there is anincreasing demand for stainless steel building panels for exteriorapplication. This metal possesses the desired and required corrosionresistance for long-time outdoor atmospheric exposure plus the requiredformability and the desired mechanical strength. Also, this metalexhibits a particularly desired bright and lustrous attractive metallicappearance that may be modified by surface treatment to effect amultitude of reflective or of non-reflective surfaces that are ideal foreither indoor or outdoor building panel applications. In consequence, itmay be seen that stainless steel is an ideal material from which one mayproduce building panels. For outdoor building panel applications it is,of course, necessary to employ relatively dull or non-reflectivefinishes, in that if such a finish is too bright its reflection of sunrays will prohibitively blind on-lookers and may actually be responsiblefor damage to adjacent property. The stainless steel most frequentlyemployed for such panels generally exhibits what is known in theindustry as a #2D or #2B sheet finish. A #2D finish is a dull coldrolled finish or one in which the flat rolled stainless steel has beencold rolled, heat treated and pickled. This finish is relativelyunattractive and consequently has fallen from demand since the primarypurpose of employing stainless steel is to provide an attractive finishas well as one that will resist corrosive attack. A #ZB finish issomewhat brighter than a #2D in that it has been bright cold rolled orpressed between ,the relatively smooth rolls of a cold rolling millafter annealing and pickling, but it does not have as high a luster as apolished finish. This material, however, is generally considered to betoo reflective and is also not particularly attractive for the desiredapplication.

In addition, both a #2D and #2B sheet finish exhibit directional stripeson their surfaces, or in other words, show the imperfections of the coldrolling in one direction, hence requiring proper alignment of the panelsboth during fabrication and installation. A particularly desirablefinish is a grit blasted finish or a finish wherein relativelyhardparticulate material of a grit size of from about 3.0 to 50 grit hasbeen propelled in a relatively uniform manner against the surface of thestainless steel so as to effect a substantially uniform 30 to 50 gritblasted finish. T effect ,such a finish by presently known commercialmeans would be prohibitively expensive in that each panel would have tobe individually grit blasted, and additionally, it would be impracticalto attempt to device means to effect the required uniformity of thepanels appearance, in that in grit blasting the grit material isgenerally and gradually broken down ,into finer grit particles;consequently, one may not elfect a uniform 30 to 50 grit finish by gritblasting the stainless steel, and attempts to accomplish such a finishby this means have not been successful in that architecturalrequirements and specifications demand a completely uniform finish foreach panel and deviation from such uniformity is readily observable oninstalled panels of this type. Other attempts to secure a uniform finishof this type have been to grit blast rolls of the cold rolling mill toeffect the desired finish on the metal surface of the relativelyhardened rolls. The stainless steel is then passed through such a milland the desired finish is embossed on the surface of such stainlesssteel. This method has also proved to be relatively unsatisfactory inthat, although the finish imposed is one that is highly desired,reproducibility has been found to be impractical in that the rolls losetheir ability or wear smooth far before a commercial product may beefiected. In other words, once again the manufacturer is unable to meetthe desired architectural specifications of a uniform surface, andconsequently such a method has proved to be unsuccessful except asmodified in accordance with the method of the present invention.

It has now been found that by employing rolls that possess a Rockwell Chardness of at least 60 and which have been given a substantiallyuniform 7 to 90 grit finish by grinding or polishing and subsequentlygrit blasted so as to effect a substantially 14 to 18 grit finish andthen grit blasted a second time to effect the desired 30 to 50 gritfinish, such rolls may be successfully employed to produce a stripproduct that exhibits a surprisingly uniform 30 to 50 grit finishthroughout the lengths of numerous austenitic stainless steel coils.

It is accordingly the object of the present invention to provide amethod wherein a substantially uniform 30 to 50 grit blasted finish maybe produced on the surface of austenitic stainless steel strip.

It is also an object of the present invention to provide a new anduseful architectural finish for stainless steel building panels that maybe reproduced effectively so that panels produced by the present methodon one lot may be subsequently and independently produced on another lotof austenitic stainless steel.

A still further object of the present invention is to provide a methodof reproducing austenitic stainless steel building panels with a 30 to50 grit blast finish in a substantially uniform manner.

Other objects and advantageous features will be obvious from thefollowing specification:

In general, the present invention relates to the production of astainless steel fiat rolled product that possesses a substantiallyuniform 30 to 50 grit blast finish that inyolves the steps of initallyproviding one or more cold rolling mill rolls that possess a hardness ofat least 60 'Rockwell C, grinding the surface of such a roll with anabrasive so as to effect a substantially uniform to grit finish thereon,grit blasting the ground surface of the said roll with a grit that willeffect a substantially uniform 14 to 18 grit blast finish, grit blastingthe surface of said roll with a grit that will effect a substantiallyuniform 30 to 50 grit blasted finish on the surface thereof and finallycold rolling the stainless steel with the said roll so as to emboss theresulting roll finish on the surface thereof.

The reason for the reproducibility of the embossed finish of the presentinvention is not readily understood, in that to effect the grit blastedfinish to the roll without first interposing the grinding andpreliminary grit blasting steps does not effect a roll that willuniformly reproduce the desired finish. This is particularly true forreproducing the finish from lot to lot where it is necessary to employnew rolls of this nature or to re-face the original roll where the gritblasted finish deteriorates from use. The roll itself may bemanufactured from any of the hardenable steel grades that are capable ofbeing hardened on the surface thereof to a Rockwell C 60 or greater; foreX ample, such rolls are known to be fabricated from steel of thefollowing analyses:

Analysis N0. 1 Analysis No. 2

Carbon .93 Carbon .83 Manganese .40 Manganese .34 Silicon .29Phosphorous .012 Chromium 2.34 Sulfur .017 Vanadium .10 Silicon .27 IronBal. Nickel .20 Chromium 1.97 Vanadium .10 Molybdenum .22 ron Bal.

The roll, of course, is ground in a circular manner so that the grindmarks parallel the peripheral face of the roll in contrast to thehorizontal axis thereof. The grinding media may be any conventionalgrinding apparatus, such as a grinding wheel or a grinding belt, and theabrasive material itself may be any of the conventio-nl abrasivematerials employed for such purposes or any other abrasive so long as itis capable of effecting the 70 to 90 grit finish thereon. Particularlysatisfactory results have been obtained by employing an 80 grit numberC80L10ES National Grinding Wheel (manufactured by the National GrindingWheel Company of North Tonawanda, New York) on a cold rolling roll28-inch diameter-56-inch face that exhibits a roll hardness of 66/67Rockwell C. This grinding wheel is used to give a smooth uniform finishto the roll without brightness which must be free from roll chatter,wheel marks, grit marks, etc. The grinder employed may be any of theconventional apparatus. Particularly satisfactory results have beenobtained by employing a Farrel Roll Grinder (manufactured by the FarrelBirmingham Company, Ansonia, New York).

The grit blasting may be accomplished by any of the commerciallyavailable apparatus designed for this purpose. Excellent results havebeen obtained by employing the Pangborn Rotablast Machine (manufacturedby the 'Pangborn Corporation, Hagerstown, Maryland), wherein the roll isplaced within a carriage within a machine which revolves the rolls as itenters the grit blast cabinet. As the carriage enters the cabinet, thedoor closes and a power driven wheel that includes a spout, impeller,vanes and impeller case impels the grit striking the rolls and breaks upthe surface thereon. Other commercially available machines propel thegrit through means of an air blast that picks up the grit through anapplicator similar to the principle of a spray gun; however, bestresults hve been obtained by the Pangborn type machines. The initialgrit used in the second step of the method should be substantially 14 to18 grit. The preferred particles are 16 grit in size, and this size gritis available commercially. Particles of 16 grit size are about .049/.050 inch in diameter. It is preferable to employ an angular type ofgrit. The G-l6 or 16 grit Mallabrasive (trademark of PangbornCorporation applied to a hard metal abrasive) is used to roughen thesurface and imparts a rough texture to the roll. It is, of course,understood that the roll must have a hardness of at least 60 Rockwell Cin order to maintain the grit blast surface during processing and whileembossing the ultimate cold-rolled article. The exact function of theinitial or roughening grit blasting with the 16 grit material is notprecisely understood, although such grit blasting may serve in somemanner to further cold work the already hardened surface of the roll.

The length of time in which the roll is grit blasted with a 16 gritmaterial is that length of time required to effect a substantiallyuniform 16 grit finish to the roll surface. It has been found to bepreferable in obtaining optimum results to effect four passes in thePangborn machine at 2 feet per minute rotation of the roll to get thedesired effect.

The third step in treating the roll is to substantially uniformly gritblast the already grit blasted surface with 30 to 50 grit material thatwill effect a 30 to 50 grit blasted finish on the surface. 40 gritmaterial has been found to be preferred and will be most often used,since it is a standard grit used in commercial grit blasting prac tices.The 40 grit material will preferably be an angular heat treated grit.The approximate size of this material is .010/ .015 inch diameter and ispreferably a sharp angular grit which will retain the sharpness as itbreaks up into smaller particles. I have found this to be an ideal gritmaterial to use to impart to the roll the surface texture that has thedesired attractive appearance, smoothness and uniformity. Usually onepass at four feet per minute will have the desired effects. The roll isnow in condition for embossing stainless steel and may be inserted intothe cold rolling mill to treat stainless steel.

It is, of course, understood that if both rolls through which the stripor sheet stainless steel passes have been given the treatment of thepresent invention, both surfaces of the strip will be embossed with thedesired architectural finish; however, it will generally be desired toeffect such a finish to only one side of the strip since only one sidewill be employed as an architectural finish, and consequently, generallywill be desirable to eflfect such a finish to only one of the opposingwork rolls in the cold rolling mill.

Any conventional cold rolling equipment that is capable of reducing thegauge of austenitic stainless steel strip or sheet may be employed, it.being understood that the embossing roll will be one designed to fitsuch a mill. We have employed such rolls in a two-high Lewis mill(manufactured by the Lewis Foundry Company of Pittsburgh, Pa.). Thestrip is threaded to the tension reel with the mill open (with the rollsapart). When the end is secured in the reel, the tension is applied andthe rolls brought down and pressure applied. A lubricant, such asalcohol. should be used on the rolls; the strip is rolled in the regularmanner. It has been found to be desirable to omit the use of rollingoils. The rolls should be kept moist by dripping and keeping the stripWet with a material such as methyl ethyl or butyl alcohol. One pass onthe mill is generally all that is required.

The method of the present invention has been found to be applicable onlyto the austenitic type stainless steels. These steels contain from about10% to 30% chromium, less than 1% carbon, and various quantities ofaustenite stabilizers such as nickel, manganese and nitrogen that aredesigned to be present in such amounts as required to maintain anaustenitic structure at room temperature. These materials are given anAISI designation as Types 200 and 300 stainless steels. Typical examplesof such steels are AISI Types 201 and 202 and AISI Types 30 1, 302 and304 stainless steels. Many grades contain incidental additions, such asmolybdenum, columbium and titanium that affect the mechanical propertiesto some degree but do not basically afiect the austenitic structure norfundamental mechanical properties. Such steels should be distinguishedfrom ordinary low alloy and ferritic steels and from ferritic andmartensitic type stainless steels which contain chromium within the samerange as the austenitic steels but which do not contain suflicientquantities of austenite stabilizers to retain a room temperatureaustenitic structure and consequently do not have the same basicmechanical properties as the austenitic steels. Apparently, the uniquemechanical properties inherent in austenitic stainless steels arerequired for the material to be amenable to the present process.

The grit employed in the initial grinding operation and in thesubsequent grit blasting steps are the standard grit sizes as designatedby the Society of Automotive Engineers (S.A.E.). The following Table Iis a standard SAE grit size table giving the high and low limit screensizes and the minimum and maximum percentages of grit retained andpassed for a given number. The grit sizes 30, 70 and 90, as set forth inthe present specification and claims, are not set forth in the tablesince these grit sizes are not standard commercially available particlesand consequently are not set forth in the table; however, appropriateinterpolation will evolve the appropriate measurements.

6 finishes, the standard polished black Carrara glass was used as astandard at 5.6% reflection at 45 and with the refractive index of1.542.

It should be noted that all of the standard finishes exhibit differentreflectivity from the longitudinal to the transverse readings, while thearchitectural finishes showed an identical reading in both thelongitudinal and trans- TABLE I High limit screen Nominal screen Lowlimit screen Grit number Max. Screen Min. Screen Max. Screeen gritnumber grit number grit to number retained, and retained, and pass, and

percent aperture percent aperture percent aperture The 14 to 18 gritmaterial may be composed of particles of any material, regardless of howhard or soft, that will impart the desired 14 to 18 grit finish to thesteel roll. A particularly fit material has been found to be a PangbornMallabrasive material (Pangborn Corporation, Hagerstown, Maryland). Suchmaterial is composed of a hard brittle iron base product which has beenreduced to the 14 to 18 grit size.

The 3.0 to 50 grit blast finish also may be accomplished by any materialwith sufiicient mechanical properties to impose such a 30 to 50 gritblast finish. I have obtained particularly desirable results byemploying Pangborn Angular grit (trademark of Pangborn Corporation,Hagerstown, Maryland), such angular grit providing an abrasive withhard, sharp cutting edges.

Gloss meter readings were taken on various grades of standard finishedsheet material commonly employed as architectural panel finishes on Type302 and Type 202 stainless steels. Similar readings were also taken onthe architectural finish applied to Type 302 stainless steel inaccordance with the method of the present invention. Table II belowshows the results of such readings.

The gloss meter employed was a photoelectric gloss meter, Model 660,manufactured by Photovolt Corporation, 95 Madison Avenue, New York 16,New York. To establish 100% reflectivity, a micropolished Type 302stainless steel that was ground and polished with felt pads was regardedas having 70% reflectivity which is considered standard in the industry.For the lower reflected surfaces, #ZD, #2B and the present architecturalverse directions. It is also to be noted that the architectural finishof the present invention ranges in reflectivity to from less than tomore than a #2D finish. This is significant in that the architecturalfinish is far more attractive than the #2D finish and yet may possesseither slightly less or slightly more reflectivity than that finish. Itis to be noted that a #213 finish possesses higher reflectivity than a#3, and in fact, higher reflectivity than a #4 finish which is known tobe a relatively bright and reflective finish.

I claim:

1. The method of providing an architectural finish to the surface offlat cold rolled austenitic stainless steel which comprises the steps:

(a) providing a steel roll that possesses a hardness of approximately66/67 Rockwell C,

(b) grinding the surface of said roll with an grit abrasive so as toeffect a uniform 80 grit finish thereon,

(c) grit blasting the surface of said roll with No. 16 grit particles soas to effect a uniform 16 grit, grit grit blasted finish thereon,

(d) grit blasting the surface of said roll with No. 40 grit particles soas to effect a uniform 40 grit, gri blasted finish thereon,

(e) inserting said roll as a work roll in a cold rolling mill androlling said flat cold rolled austenitic stainless steel through saidcold rolling mill so as to enrboss on the surface of said stainlesssteel the surface finish of said roll.

2. The method of providing an architectural finish to the surface offlat cold rolled austenitic stainless steel which comprises the steps:

(a) providing a hardenable steel roll that possesses a hardness of atleast 60 Rockwell C,

(b) grinding the surface of said roll with a 70 to grit abrasive so asto effect a uniform 70 to 90 grit finish thereon,

(a) grit blasting the surface of said roll with particles of from 14grit to 18 grit so as to effect a uniform grit finish thereon,

(d)grit blasting the surface of said roll with No. 30 to 50 gritparticles so as to effect a uniform 30 to 50 grit finish thereon, and

(e) inserting said roll as a work roll in a cold rolling mill androlling said flat cold rolled austenitic stainless steel through saidcold rolling mill so as to emboss on the surface of said stainless steelthe surface finish of said roll.

3. The method of providing an architectural finish to 7 the surface offlat cold rolled austenitic stainless steel which comprises the stepsz(a) providing a hardenable steel roll that possesses a hardness of atleast 60 Rockwell C,

(b) grinding the surface of said roll with a 70 to 90 grit abrasive soas to effect a uniform 70 to 90 grit finish thereon,

(c) grit blasting the surface of said roll with particles of from 14grit to 18 grit so as to effect a uniform grit finish thereon,

(d) grit blasting the surface of said roll with No. 30 to 50 gritparticles so as to effect a uniform 30 to 50 grit finish thereon, and

(e) inserting said roll as a work roll in a cold rolling mill androlling said flat cold rolled austenitic stainless steel through saidcold rolling mill While applying alcohol as a lubricant so as to embosson the surface of said stainless steel the surface finish of said roll.

4. The method of providing an architectural finish to the surface offiat cold rolled stainless steel which comprises the steps:

(a) providing a pair of hardenable steel rolls, each of which possessesa surface hardness of at least 60 Rockwell C,

(b) grinding the surface of each of said rolls with a 70 to 90 gritabrasive so as to effect a uniform 70 to 90 grit finish on the surfaceof each of said rolls.

() grit blasting the surface of each of said rolls with grit particlesof a grit size of from 14 to 18 grit so as to effect a uniform gritfinish on the surface of each of said rolls,

(d) grit blasting the surface of each of said rolls with No. 30 to 50grit particles so as to effect a uniform 30 to 50 grit finish on thesurface of each of said rolls, and

(e) inserting said rolls as the opposing work rolls in a cold rollingmill and rolling said fiat cold rolled austenitic stainless steelthrough said cold rolling mill so as to emboss on the opposing surfaceof said stainless steel the surface finish of said rolls.

5. The method of providing an architectural finish to the work surfaceof hardened sheet or ship mill rolls and which surface shall impresscomplimentary finishes on sheet or strip during continued use thereof,the method comprising:

(a) grinding the surface of said roll With a 70 to 90 grit abrasive soas to effect a uniform 70 to 90 grit finish thereon,

(b) grit blasting the surface of said roll with particles of from 14grit to 18 grit so as to effect a uniform grit finish thereon, and

(c) grit blasting the surface of said roll with number 30 to gritparticles so as to effect a uniform 30 to 50 grit finish thereon.

6. The method of providing an architectural finish to the work surfaceof sheet or strip mill rolls having a hardness of at least Rockwell Cand which surface shall impress complimentary finishes on sheet or stripduring continued use thereof, the method comprising:

(a) grinding the surface of said roll with a to grit abrasive so as toeffect a uniform 70 to 90 grit finish thereon,

(b) grit blasting the surface of said roll With particles of from 14grit to 18 grit so as to effect a uniform grit finish thereon, and

(c) grit blasting the surface of said roll with number 30 to 50 gritparticles so as to effect a uniform 30 to 50 grit finish thereon.

References Cited in the file of this patent UNITED STATES PATENTS

